When stock,,,the 4.3 Syclone runs 14 psi.Mainly because the heads are restrictive.

W/a smaller tubo,it only made 386 HP & 550 ft lbs of torque.
21 psi.
Only makes power to 4400 rpm = weak a$$ camshaft.
It goes to show you that a great flowing head can do on the 4.2.


MBHD

12 port SDS EFI